1. Field of Invention
This invention relates to a method of cleaning a component in a processing chamber of a plasma processing apparatus used in the production of semiconductor devices, and to a method of producing semiconductor devices utilizing the cleaning method.
2. Description of Related Art
Plasma processing apparatus are widely used in production of semiconductor devices. In particular, plasma processing apparatus having a processing chamber provided with parallel-plate electrodes is generally used in dry etching and chemical vapor deposition (CVD). In such plasma processing apparatus, an electrode facing a semiconductor wafer, which forms one of the parallel-plate electrodes, is used as an essential component in the processing chamber.
As an example, dry etching of a silicon oxide film used as an insulating material of a semiconductor device will now be described. This process utilizes plasma formed using a process gas atmosphere containing one or more fluorocarbon gasses.
FIG. 1 is a schematic cross-sectional view of a dry etching apparatus, which is an example of the plasma processing apparatus, used to etch silicon oxide films. A lower electrode 109 having an electrostatic chuck 108 to support a semiconductor wafer 107 is positioned at the bottom of a processing chamber, or a reaction chamber, 200. An upper electrode (a counter electrode) 100 facing the wafer 107 placed on the lower electrode 109 is positioned in a housing 111 at the top of the processing chamber 200. The upper electrode 100 and the lower electrode 109 constitute parallel-plate electrodes. A region between the parallel plate electrodes functions as a processing zone, or a reaction zone, 106.
The upper electrode 100 includes an upper electrode table 104, a gas-dispersing element 103, a cooling plate 102, and an electrode plate 101. The electrode plate 101 directly faces the processing zone 106 and functions as the electrode to generate plasma in the processing zone 106.
FIG. 2 is a plan view of the electrode plate 101. Referring to FIG. 2, the electrode plate 101 has a plurality of gas nozzles (small holes) 120 and also functions as a showerhead that uniformly supplies the process gas to the processing zone 106.
The upper electrode table 104 has a gas inlet 105 for introducing a process gas (etching gas), which is a mixture of one or more fluorocarbon gasses and some additional gasses. The process gas is uniformly supplied to the reaction zone 106 through the gas nozzles 120 of the electrode plate 101 via the gas-dispersing element 103 and the cooling plate 102. A pump (not shown) evacuates the process gas supplied to the processing zone 106 with a controlled pumping speed and a process gas atmosphere, or an etching gas atmosphere, with a controlled gas pressure is provided within the processing zone 106.
RF (radio frequency) power is applied between the electrode plate 101 of the upper electrode 100 and the lower electrode 109 from an RF power source 130 through an RF power splitter 131. Plasma of the process gas containing fluorocarbon gas or gasses (fluorocarbon plasma) is subsequently generated within the processing zone 106. Thus, the surface of the semiconductor wafer 107 is etched by active species such as radicals and ions generated within the plasma.
An upper quartz plate 110 covers the periphery of the upper electrode 100, and a lower quartz plate 112 surrounds the periphery of the lower electrode 109. In this configuration, the plasma is concentrated between the parallel-plate electrodes 100 and 109.
The size of the electrode plate 101 depends on the size of the semiconductor wafer 107 to be processed. For example, for an 8-inch semiconductor wafer 107, an electrode plate 101 having a diameter of 280 mm and a thickness of 5 mm may be used. In such a case, as shown in FIG. 2, the electrode plate 101 is provided with 640 gas nozzles 120 with a diameter of, for example, 0.5 mm.
The electrode plate 101 of the upper electrode 100 may be constructed from various materials such as aluminum or aluminum alloy with anodized surface oxide film (alumite film), carbon, or silicon. The selection of the material of the electrode plate depends on, among other things, the type of plasma generation.
For a cathode-coupled parallel-plate type plasma apparatus in which RF power is supplied to the lower electrode, aluminum or aluminum alloy with surface anodized oxide film (hereafter referred to as anodized aluminum) is commonly used. On the other hand, for an anode-couple parallel-plate type plasma apparatus in which RF power is supplied to the upper electrode, or a split-coupled parallel-plate type plasma apparatus in which RF power is supplied both to the lower and the upper electrode, carbon or silicon is used.
In the anode-coupled and the split-coupled type apparatus, the electrode plate 101 is bombarded with high-energy ions generated in the plasma, and the material of the electrode plate 101 is sputtered. If the electrode plate 101 is made from anodized aluminum, the semiconductor device processed in the plasma apparatus is contaminated with sputtered aluminum and degraded.
Although fluorocarbon plasma significantly erodes an electrode plate made from carbon or silicon, these materials do not include metal that degrades the semiconductor device. Among them, silicon is especially preferable to minimize the degradation of the semiconductor devices, because it is the main material of the semiconductor devices and can be highly purified to remove virtually all metals.
Because fluorocarbon plasma significantly erodes the electrode plate made from carbon or silicon, however, the life of these electrode plates determined by the erosion is short. That is, the shape of the electrode plate quickly changes during successive processing of a plurality of wafers and the etching characteristics changes. When the change of the etching characteristics exceeds an acceptable range, the electrode plate must be replaced with a new one.
In addition, because products produced by the reaction in the plasma deposit on components in the processing chamber, the components must be periodical cleaned or replaced with new ones. In particular, extremely high cleanness is required for the electrode plate 101 of the upper electrode 100, because it directly faces the semiconductor wafer 107.
Previously, a carbon or silicon electrode plate is used continuously to its life without cleaning it and then replaced with a new one, because the life of carbon or silicon electrode plate determined by the erosion is short. It was found that, however, the life of the carbon electrode plate is too short.
Compared with carbon, silicon has a lower erosion rate. Therefore, it is expected that a silicon electrode plate have a longer life compare with a carbon electrode plate.
However, this inventor has found that the continuous usage of a silicon electrode plate is limited by the deposition of reaction products within the gas nozzles before the life determined by the erosion. That is, before the etching characteristics are degraded due to the erosion, a large number of particles are generated from the reaction products deposited in the gas nozzles. Such particles significantly decrease the yield of the semiconductor devices processed in the etching apparatus, and make it impossible to continue the usage of the electrode plate.
This inventor has also found that the reaction products deposited on a silicon electrode plate cannot be removed by cleaning methods that are used for cleaning components formed with other materials. Therefore, it was impossible to clean and re-use the silicon electrode plate after it is used until the reaction products are deposited and particles are generated. In other words, although the life, or the intrinsic life, of the silicon electrode plate determined by the erosion is long, the effective life is limited by the deposition of reaction products.
In fact, this inventor has found that the effective life of the silicon electrode plate is about the same as that of the carbon electrode plate, which has much shorter intrinsic life. Thus, it is required to keep a large number of electrode plates as replacement parts so that the electrode plate reached the effective life can be readily replaced, even though the electrode plate is made from silicon that has a long intrinsic life. As a result, the production cost and the consumption of natural resourced required for the replacement parts are increased.
Such findings by this inventor are also described in Japanese Unexamined Patent Application Publication No. 2002-231699, which is incorporated by reference in its entirety.